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Corresponding author: Aditya V. Maheshwari, MD, Department of Orthopaedic Surgery and Rehabilitation Medicine, SUNY Downstate Medical Center, 450 Clarkson Ave., MSC 30, Brooklyn, NY 11203.
We report a case of heterotopic ossification formation 6 years after a revision carpal tunnel release in a 46-year-old woman, causing new-onset mixed ulnar and median nerve compression symptoms. The patient underwent excision of the heterotopic ossification mass along with decompression of the median and ulnar nerves, and postoperative radiation. Four years after treatment, the patient was completely asymptomatic with full range of motion in her hand and wrist.
Carpal tunnel syndrome (CTS) is the most common peripheral compression neuropathy with a reported incidence of carpal tunnel release (CTR) surgery of 2 to 4 cases per 1,000 population
We present a case of HO after revision CTR causing new-onset median and ulnar compression neuropathy.
Case Report
A 46-year-old right-handed, morbidly obese woman with asthma presented with a painful wrist mass and numbness, tingling, and weakness in all her digits. She had an ipsilateral CTR at a different institution about 6 years previously, followed by a revision CTR with external neurolysis of the median nerve 5 months later because of recurrent symptoms and positive findings on EMG. The second operative note described the median nerve as extensively wrapped in tenosynovium that was debrided. The pathology report from the excised tissue was benign fibroadipose tissue with tenosynovium. She had complete resolution of her symptoms after the surgery. Plain radiographs before these surgeries did not show any abnormalities. Apart from these 2 surgeries, she denied any trauma to the wrist. A year after her second surgery, she noticed some peri-incisional fullness evolving into a mass. The mass slowly enlarged and hardened to the presenting size and texture with pain and stiffness. Five years after the second procedure, she started having numbness and tingling in all her digits, beginning in her radial 3 digits.
On examination of her wrist, the surgical scar was well healed. There was a 7 × 6-cm hard, nonmobile volar mass proximal to the wrist crease (Fig. 1). The mass was well defined, did not change in size with direct pressure or limb elevation, and did not transilluminate. She had numbness of about 20% to 60% in the ulnar and median nerve distributions and 2-point discrimination greater than 10 mm. There was a positive Tinel sign directly over the mass. Wrist range of motion was restricted in all planes and grip strength was reduced to 30% of the contralateral side. She had a positive Allen test consistent with ulnar artery compression. Plain radiographs, magnetic resonance imaging (MRI), and computed tomography scan demonstrated a complex, well-defined, mineralized volar wrist mass (Figure 2, Figure 3, Figure 4). Laboratory work-up was normal including alkaline phosphatase level. Based on the benign-appearing imaging studies, indolent clinical course, and history of multiple surgeries, a differential diagnosis of HO was primarily considered over an extraskeletal chondroma or osteochondroma, Nora lesion, and synovial chondromatosis/osteochondromatosis. The other differential diagnoses for mineralized soft tissue masses in this location included synovial sarcoma, parosteal and extraskeletal osteosarcoma, parasitic and injection granuloma, and systemic processes such as tumor calcinosis, gout, pseudogout, and hyperparathyroidism.
Figure 2A Anteroposterior and B lateral radiographs of the right wrist demonstrate a large complex 7-cm ossified mass in the volar aspect of the wrist.
Figure 3Axial computed tomography images at the level of the distal radioulnar joint in A soft tissue and B bone windows show a large complex mineralized mass (arrows) with primarily peripheral mature ossification and with central fat (∗) and soft tissue attenuation elements (arrowheads). Note the volar displacement of the carpal tunnel structures (red star).
Figure 4Spin echo A axial T1, B axial T2, C coronal T2 fat saturation, and D C+ axial T1 MRI at the level of the distal radioulnar joint show a large complex mass (arrows) with heterogeneous signal containing adipose elements (∗) and demonstrate areas of heterogeneous enhancement (arrowheads). There is extensive edema along the ossified parts of the mass. The carpal tunnel contents are displaced volarly and radially (red star).
The patient underwent excision of the mass using a curvilinear incision incorporating her prior incision to gain access to both the radial and the ulnar sides of the volar wrist. Initially, the interval between the flexor carpi radialis and the brachioradialis tendons was explored and the superficial radial nerve and radial vessels were identified and protected. The mass was deep to the superficial flexor tendons but mixed in with the deep flexor tendons. The mass involved the pronator quadratus and, in some areas, was adherent to the periosteum of the radius, the distal interosseous membrane, and the long flexor tendons. The median nerve and the ulnar neurovascular bundle were adherent, stretched and displaced by the mass. The ulnar nerve was displaced medially and the median nerve was pushed volarly and laterally along with the contents of the carpal tunnel. The median nerve was dissected and freed from the capsule of the mass. Redundant scar tissue was excised in and around the carpal tunnel and the median nerve was decompressed completely. The ulnar neurovascular bundle was then explored through the Guyon canal. There was no compression found within the canal, and the mass effect was limited to the region proximal to the Guyon canal. The mass was sharply dissected from the bone subperiosteally and bluntly from the surrounding long flexors. The excised mass measured about 8 × 6 × 4 cm (Fig. 5). Once decompressed, the ulnar artery was pulsatile and patent. The pathology diagnosis of the excised tissue was HO with no evidence of malignancy (Fig. 6).
Figure 5Intraoperative clinical photographs of the volar wrist mass, which was adherent to A the bone and the flexor tendon mass. B Mass after en bloc resection. Cut surface revealed tan white firm bone with a thin layer of fibrocartilaginous soft tissue at the periphery. C The median nerve after mass removal. (The hand is toward the right side of these pictures.)
Figure 6Hematoxylin-eosin stains show the lesion is composed of metaplastic mature trabecular bone (arrow) with fatty marrow and a thin layer of metaplastic fibrocartilaginous tissue (double arrows) over the surface. A Magnification × 40. B Higher magnification (×100) shows mature trabecular bone and fatty marrow (red arrow).
After surgery, the patient had immediate improvement in her median and ulnar nerve symptoms as well as return of the ulnar artery pulse with a normal Allen test. She had external beam radiation therapy on postoperative day 2 (single dose of 700 cGy). The patient was allergic to all nonsteroidal anti-inflammatory drugs (NSAIDs), including indomethacin, and none were given. She also completed a course of hand therapy. At her last follow-up 4 years after this surgery, the patient had full strength and sensation of her wrist and digits in all distributions along with a full range of motion. Repeat plain radiographs showed no recurrence of the mass (Fig. 7).
Figure 7Four-year follow-up postoperative radiographs A anteroposterior and B lateral views of the right wrist demonstrate no residual radiological mass or mineralization.
Heterotopic ossification is a diverse pathological process resulting in the formation of extraskeletal bone in soft tissues. Etiologically, it can be acquired or genetic.
Acquired HO commonly occurs secondary to trauma and has been described following arthroplasty, arthroscopy, trauma and trauma surgeries, central nervous system injury and inflammation, and burns. Fibrodysplasia ossificans progressiva, progressive ossific heteroplasia, and ankylosing spondylitis
It is important to distinguish them because they may have a high rate of recurrence after excision and subsequently an aggressive clinical course, in contrast to the acquired conditions, which have a better prognosis.
Etiologies linked to formation of HO include genetic pathways with bone morphogenic protein (BMP) signaling, hypoxia-inducible factors, inflammatory cytokines, and retinoid acid receptor signaling.
theorized that demineralized bone matrix contained BMPs that stimulated mesenchymal stem cells to differentiate into osteoblasts. Several inductive agents have been implicated in the process of bone formation including BMPs 2, 4, and 9.
Local trauma or systemic inflammation disrupts the normal balance of bone mineralization and creates a pathological cascade leading to abnormal bone growth in receptive tissue. It is not clear why only some patients develop HO, but a plausible explanation could be an extrinsic stimulus activating a combination of these pathways in conjunction with the patient's genetic makeup.
Heterotopic ossification has also been reported as a cause of peripheral nerve compression and/or encasement at multiple sites including the ulnar nerve at the elbow.
Heterotopic ossification is rarely found at the wrist, but has been reported as the cause of primary CTS in patients with underlying ankylosing spondylitis
To the best of our knowledge, postoperative HO has never been described following CTR causing a recurrence of symptoms. We believe that her multiple CTR surgeries locally traumatized her wrist soft tissues predisposing her to HO formation, as described after other orthopedic surgeries, commonly around the hip and elbow.
the role of radiation and NSAIDs for HO prevention and treatment in the wrist has not been studied. Thus, we planned a similar treatment in our patient, although she could not tolerate NSAIDs.
Whereas other mineralized soft tissue masses were considered in the differential,
HO was the working diagnosis of the mass based on the characteristic radiological features, the insidious onset of symptoms, and a history of prior surgeries. The definitive diagnosis was made only after tissue histology and pathological examination. A biopsy was not performed before excision because the history and work-up indicated a benign process. Regardless, the treatment would have been marginal excision of the mass. This would not have changed based on a preexcision tissue diagnosis. However, if there is concern for malignancy or the diagnosis is unclear, a biopsy should be performed. The patient underwent successful resection of the mass with resolution of her symptoms and there was no recurrence at her 4-year follow-up visit.
Radiologically, HO typically appears as a well-demarcated radiodense mass with a zonal phenomenon based on the stage of the maturation process.
In early to intermediate stages of HO, MRI and bone scan studies might be misleading and not helpful because diffuse inflammation can lead to mixed heterogeneous findings concerning for malignancy.
However, in the late stage of HO, once the mass matures and ossifies, the MRI shows a central signal mimicking normal ossified bone and fatty marrow. Computed tomography and radiographs will show a more peripheral mineralization in contrast to an osteosarcoma, which has a more central mineralization.
Although rare, surgeons should be aware of this complication as a potential cause of persistent or new-onset neuropathy, especially after multiple surgeries. A thorough physical examination along with the appropriate imaging is required if a mass is suspected as the cause of recurrent symptoms.
References
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Incidence of carpal tunnel release: trends and implications within the United States ambulatory care setting.
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